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Sielaff H, Zhao ZW. Visualizing, quantifying and mapping chromatin remodelers at work with single-molecule and single-cell imaging. Int J Biochem Cell Biol 2024; 176:106667. [PMID: 39362301 DOI: 10.1016/j.biocel.2024.106667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2024] [Revised: 08/26/2024] [Accepted: 09/23/2024] [Indexed: 10/05/2024]
Abstract
Chromatin remodeling, carried out by four major subfamilies of ATP-dependent remodeler complexes across eukaryotes, alleviates the topological challenge posed by nucleosomes to regulate genome access. Recently, single-molecule and single-cell imaging techniques have been widely employed to probe this crucial process, both in vitro and in cellulo. Herein, we provide an integrated account of key recent efforts that leverage these approaches to visualize, quantify and map chromatin remodelers at work, elucidating diverse aspects of the remodeling process in both space and time, including molecular mechanisms of DNA wrapping/unwrapping, nucleosome translocation and histone exchange, dynamics of chromatin binding/target search and their intranuclear organization into hotspots or phase condensates, as well as functional coupling with transcription. The mechanistic insights and quantitative parameters revealed shed light on a multi-modal yet shared landscape for regulating remodeling across molecular and cellular scales, and pave the way for further interrogating the implications of its misregulation in disease contexts.
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Affiliation(s)
- Hendrik Sielaff
- Department of Chemistry, Faculty of Science, National University of Singapore, Singapore 119543, Singapore; Centre for BioImaging Sciences (CBIS), Faculty of Science, National University of Singapore, Singapore 117557, Singapore.
| | - Ziqing Winston Zhao
- Department of Chemistry, Faculty of Science, National University of Singapore, Singapore 119543, Singapore; Centre for BioImaging Sciences (CBIS), Faculty of Science, National University of Singapore, Singapore 117557, Singapore; Mechanobiology Institute (MBI), National University of Singapore, Singapore 117411, Singapore; Integrative Sciences and Engineering Programme (ISEP), National University of Singapore, Singapore 119077, Singapore.
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Godschalk R, Faulk C, LaRocca J, van Benthem J, Marchetti F. Epigenotoxicity: Decoding the epigenetic imprints of genotoxic agents and their implications for regulatory genetic toxicology. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2024. [PMID: 39262275 DOI: 10.1002/em.22626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2024] [Revised: 08/16/2024] [Accepted: 08/20/2024] [Indexed: 09/13/2024]
Abstract
Regulatory genetic toxicology focuses on DNA damage and subsequent gene mutations. However, genotoxic agents can also affect epigenetic marks, and incorporation of epigenetic data into the regulatory framework may thus enhance the accuracy of risk assessment. Additionally, epigenetic alterations may identify non-genotoxic carcinogens that are not captured with the current battery of tests. Epigenetic alterations could also explain long-term consequences and potential transgenerational effects in the absence of DNA mutations. Therefore, at the 2022 International Workshops on Genotoxicity Testing (IWGT) in Ottawa (Ontario, Canada), an expert workgroup explored whether including epigenetic endpoints would improve regulatory genetic toxicology. Here we summarize the presentations and the discussions on technical advancements in assessing epigenetics, how the assessment of epigenetics can enhance strategies for detecting genotoxic and non-genotoxic carcinogens and the correlation between epigenetic alterations with other relevant apical endpoints.
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Affiliation(s)
- Roger Godschalk
- Department of Pharmacology and Toxicology, School for Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, The Netherlands
| | | | | | - Jan van Benthem
- National Institute for Public Health and the Environment, Bilthoven, The Netherlands
| | - Francesco Marchetti
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Ontario, Canada
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Engl W, Kunstar-Thomas A, Chen S, Ng WS, Sielaff H, Zhao ZW. Single-molecule imaging of SWI/SNF chromatin remodelers reveals bromodomain-mediated and cancer-mutants-specific landscape of multi-modal DNA-binding dynamics. Nat Commun 2024; 15:7646. [PMID: 39223123 PMCID: PMC11369179 DOI: 10.1038/s41467-024-52040-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2023] [Accepted: 08/22/2024] [Indexed: 09/04/2024] Open
Abstract
Despite their prevalent cancer implications, the in vivo dynamics of SWI/SNF chromatin remodelers and how misregulation of such dynamics underpins cancer remain poorly understood. Using live-cell single-molecule tracking, we quantify the intranuclear diffusion and chromatin-binding of three key subunits common to all major human SWI/SNF remodeler complexes (BAF57, BAF155 and BRG1), and resolve two temporally distinct stable binding modes for the fully assembled complex. Super-resolved density mapping reveals heterogeneous, nanoscale remodeler binding "hotspots" across the nucleoplasm where multiple binding events (especially longer-lived ones) preferentially cluster. Importantly, we uncover distinct roles of the bromodomain in modulating chromatin binding/targeting in a DNA-accessibility-dependent manner, pointing to a model where successive longer-lived binding within "hotspots" leads to sustained productive remodeling. Finally, systematic comparison of six common BRG1 mutants implicated in various cancers unveils alterations in chromatin-binding dynamics unique to each mutant, shedding insight into a multi-modal landscape regulating the spatio-temporal organizational dynamics of SWI/SNF remodelers.
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Affiliation(s)
- Wilfried Engl
- Department of Chemistry, Faculty of Science, National University of Singapore, Singapore, 119543, Singapore
- Centre for BioImaging Sciences, Faculty of Science, National University of Singapore, Singapore, 117557, Singapore
| | - Aliz Kunstar-Thomas
- Department of Chemistry, Faculty of Science, National University of Singapore, Singapore, 119543, Singapore
- Centre for BioImaging Sciences, Faculty of Science, National University of Singapore, Singapore, 117557, Singapore
| | - Siyi Chen
- Department of Chemistry, Faculty of Science, National University of Singapore, Singapore, 119543, Singapore
- Centre for BioImaging Sciences, Faculty of Science, National University of Singapore, Singapore, 117557, Singapore
| | - Woei Shyuan Ng
- Department of Chemistry, Faculty of Science, National University of Singapore, Singapore, 119543, Singapore
- Centre for BioImaging Sciences, Faculty of Science, National University of Singapore, Singapore, 117557, Singapore
| | - Hendrik Sielaff
- Department of Chemistry, Faculty of Science, National University of Singapore, Singapore, 119543, Singapore
- Centre for BioImaging Sciences, Faculty of Science, National University of Singapore, Singapore, 117557, Singapore
| | - Ziqing Winston Zhao
- Department of Chemistry, Faculty of Science, National University of Singapore, Singapore, 119543, Singapore.
- Centre for BioImaging Sciences, Faculty of Science, National University of Singapore, Singapore, 117557, Singapore.
- Mechanobiology Institute, National University of Singapore, Singapore, 117411, Singapore.
- Integrative Sciences and Engineering Programme, National University of Singapore, Singapore, 119077, Singapore.
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Nordenskiöld L, Shi X, Korolev N, Zhao L, Zhai Z, Lindman B. Liquid-liquid phase separation (LLPS) in DNA and chromatin systems from the perspective of colloid physical chemistry. Adv Colloid Interface Sci 2024; 326:103133. [PMID: 38547652 DOI: 10.1016/j.cis.2024.103133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Accepted: 03/11/2024] [Indexed: 04/13/2024]
Abstract
DNA is a highly charged polyelectrolyte and is prone to associative phase separation driven by the presence of multivalent cations, charged surfactants, proteins, polymers and colloids. The process of DNA phase separation induced by positively charged species is often called DNA condensation. Generally, it refers to either intramolecular DNA compaction (coil-globule transition) or intermolecular DNA aggregation with macroscopic phase separation, but the formation of a DNA liquid crystalline system is also displayed. This has traditionally been described by polyelectrolyte theory and qualitative (Flory-Huggins-based) polymer theory approaches. DNA in the cell nucleus is packed into chromatin wound around the histone octamer (a protein complex comprising two copies each of the four histone proteins H2A, H2B, H3 and H4) to form nucleosomes separated by linker DNA. During the last decade, the phenomenon of the formation of biomolecular condensates (dynamic droplets) by liquid-liquid phase separation (LLPS) has emerged as a generally important mechanism for the formation of membraneless organelles from proteins, nucleic acids and their complexes. DNA and chromatin droplet formation through LLPS has recently received much attention by in vitro as well as in vivo studies that established the importance of this for compartmentalisation in the cell nucleus. Here, we review DNA and chromatin LLPS from a general colloid physical chemistry perspective. We start with a general discussion of colloidal phase separation in aqueous solutions and review the original (pre-LLPS era) work on DNA (macroscopic) phase separation for simpler systems with DNA in the presence of multivalent cations and well-defined surfactants and colloids. Following that, we discuss and illustrate the similarities of such macroscopic phase separation with the general behaviour of LLPS droplet formation by associative phase separation for DNA-protein systems, including chromatin; we also note cases of segregative association. The review ends with a discussion of chromatin LLPS in vivo and its physiological significance.
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Affiliation(s)
- Lars Nordenskiöld
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore.
| | - Xiangyan Shi
- Department of Biology, Shenzhen MSU-BIT University, Shenzhen 518172, China.
| | - Nikolay Korolev
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
| | - Lei Zhao
- Department of Biology, Shenzhen MSU-BIT University, Shenzhen 518172, China
| | - Ziwei Zhai
- Department of Biology, Shenzhen MSU-BIT University, Shenzhen 518172, China
| | - Björn Lindman
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore; Physical Chemistry, University of Lund, P.O. Box 124, S-221 00 Lund, Sweden; Coimbra Chemistry Centre, Department of Chemistry, University of Coimbra, Rua Larga, 3004-535 Coimbra, Portugal.
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Seif E, Francis NJ. A Two-Step Mechanism for Creating Stable, Condensed Chromatin with the Polycomb Complex PRC1. Molecules 2024; 29:323. [PMID: 38257239 PMCID: PMC10821450 DOI: 10.3390/molecules29020323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 12/26/2023] [Accepted: 01/05/2024] [Indexed: 01/24/2024] Open
Abstract
The Drosophila PRC1 complex regulates gene expression by modifying histone proteins and chromatin architecture. Two PRC1 subunits, PSC and Ph, are most implicated in chromatin architecture. In vitro, PRC1 compacts chromatin and inhibits transcription and nucleosome remodeling. The long disordered C-terminal region of PSC (PSC-CTR) is important for these activities, while Ph has little effect. In cells, Ph is important for condensate formation, long-range chromatin interactions, and gene regulation, and its polymerizing sterile alpha motif (SAM) is implicated in these activities. In vitro, truncated Ph containing the SAM and two other conserved domains (mini-Ph) undergoes phase separation with chromatin, suggesting a mechanism for SAM-dependent condensate formation in vivo. How the distinct activities of PSC and Ph on chromatin function together in PRC1 is not known. To address this question, we analyzed structures formed with large chromatin templates and PRC1 in vitro. PRC1 bridges chromatin into extensive fibrillar networks. Ph, its SAM, and SAM polymerization activity have little effect on these structures. Instead, the PSC-CTR controls their growth, and is sufficient for their formation. To understand how phase separation driven by Ph SAM intersects with the chromatin bridging activity of the PSC-CTR, we used mini-Ph to form condensates with chromatin and then challenged them with PRC1 lacking Ph (PRC1ΔPh). PRC1ΔPh converts mini-Ph chromatin condensates into clusters of small non-fusing condensates and bridged fibers. These condensates retain a high level of chromatin compaction and do not intermix. Thus, phase separation of chromatin by mini-Ph, followed by the action of the PSC-CTR, creates a unique chromatin organization with regions of high nucleosome density and extraordinary stability. We discuss how this coordinated sequential activity of two proteins found in the same complex may occur and the possible implications of stable chromatin architectures in maintaining transcription states.
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Affiliation(s)
- Elias Seif
- Institut de Recherches Cliniques de Montréal, 110 Avenue des Pins Ouest, Montréal, QC H2W 1R7, Canada;
| | - Nicole J. Francis
- Institut de Recherches Cliniques de Montréal, 110 Avenue des Pins Ouest, Montréal, QC H2W 1R7, Canada;
- Division of Experimental Medicine, McGill University, 1001 Decarie Boulevard, Montréal, QC H4A 3J1, Canada
- Département de Biochimie et Médecine Moléculaire, Université de Montréal, 2900 Boulevard Edouard-Montpetit, Montréal, QC H3T 1J4, Canada
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Uversky VN. Biological Liquid-Liquid Phase Separation, Biomolecular Condensates, and Membraneless Organelles: Now You See Me, Now You Don't. Int J Mol Sci 2023; 24:13150. [PMID: 37685957 PMCID: PMC10488282 DOI: 10.3390/ijms241713150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Accepted: 08/18/2023] [Indexed: 09/10/2023] Open
Abstract
Liquid-liquid phase separation (LLPS, also known as biomolecular condensation) and the related biogenesis of various membraneless organelles (MLOs) and biomolecular condensates (BMCs) are now considered fundamental molecular mechanisms governing the spatiotemporal organization of the intracellular space [...].
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Affiliation(s)
- Vladimir N Uversky
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA
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Unveiling the Machinery behind Chromosome Folding by Polymer Physics Modeling. Int J Mol Sci 2023; 24:ijms24043660. [PMID: 36835064 PMCID: PMC9967178 DOI: 10.3390/ijms24043660] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2023] [Revised: 02/06/2023] [Accepted: 02/09/2023] [Indexed: 02/16/2023] Open
Abstract
Understanding the mechanisms underlying the complex 3D architecture of mammalian genomes poses, at a more fundamental level, the problem of how two or multiple genomic sites can establish physical contacts in the nucleus of the cells. Beyond stochastic and fleeting encounters related to the polymeric nature of chromatin, experiments have revealed specific, privileged patterns of interactions that suggest the existence of basic organizing principles of folding. In this review, we focus on two major and recently proposed physical processes of chromatin organization: loop-extrusion and polymer phase-separation, both supported by increasing experimental evidence. We discuss their implementation into polymer physics models, which we test against available single-cell super-resolution imaging data, showing that both mechanisms can cooperate to shape chromatin structure at the single-molecule level. Next, by exploiting the comprehension of the underlying molecular mechanisms, we illustrate how such polymer models can be used as powerful tools to make predictions in silico that can complement experiments in understanding genome folding. To this aim, we focus on recent key applications, such as the prediction of chromatin structure rearrangements upon disease-associated mutations and the identification of the putative chromatin organizing factors that orchestrate the specificity of DNA regulatory contacts genome-wide.
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